For me, I silently recalled the mysterious shadows I had seen creeping on board the Pequod during the dim Nantucket dawn, as well as the enigmatical hintings of the unaccountable Elijah.
Had you stepped on board the Pequod at a certain juncture of this post-mortemizing of the whale; and had you strolled forward nigh the windlass, pretty sure am I that you would have scanned with no small curiosity a very strange, enigmatical object, which you would have seen there, lying along lengthwise in the lee scuppers.
There are no more uses of "enigma" in the book.
Show samples from other sources
As Churchill said about Russia, it is a riddle, wrapped in a mystery, inside an enigma.